The present invention relates to a scheme of avoiding a transmission delay caused by waiting for transmission of emergency information in an ITS (intelligent transportation system) which supports both of emergency information and various nonemergency service information.
As means for realizing a multimode wireless communication scheme, there is known a cognitive wireless communication. The cognitive wireless communication is a concept of a wireless communication scheme which manages wireless schemes and a usage status of radio waves, changes a parameter used in transmission and reception by a network and a wireless node to avoid interference, and enables efficient communications.
In the cognitive wireless communication, all of wireless communication states are recognized on the network side. Accordingly, no waiting state occurs because a newly-switched channel is already in a usable state. However, it is necessary to manage and control all of the wireless communication states on the network side, resulting in a problem of an increased system scale (development and maintenance costs).
In a narrow band wireless system compliant with the wireless LAN standard (IEEE802.11), if detecting radio waves are transmitted from peripheral devices, it is necessary to stop wireless transmission at the channel (wireless communication band). Thus, there is a possibility that a waiting state of transmission occurs. Such kind of systems have a problem to avoid a waiting state of emergency wireless communications.
Japanese Unexamined Patent Publication No. 2007-116672 provides a multimode wireless communication device in which a multimode wireless terminal includes: a reconfigurable signal processing unit which switches a wireless communication scheme; a controlling unit which gives a switching instruction of the communication scheme and an instruction of a switching method of the communication scheme to the reconfigurable signal processing unit on the basis of a combination of the switching methods of the communication scheme; a switch setting determination unit which obtains communication environment information from the controlling unit, obtains a switch setting determination coefficient from a determination information storing unit, determines a combination, and gives an instruction of the combination to the controlling unit; and a determination information storing unit which holds the switch setting determination coefficient. The multimode wireless communication device is compliant with a plurality of types of wireless communication schemes, and performs communications while switching the communication scheme, so that a switching method of an optimum wireless communication scheme can be automatically selected in accordance with communication environments.
Further, in Japanese Unexamined Patent Publication No. 2008-131574, a controlling unit calculates an index value indicating an impact of interference of its node on adjacent nodes on the basis of communication load information of its node and all of the adjacent nodes and communication capacity information available for its node, exchanges a routing table in which the index values relating to the respective nodes are stored with other nodes, evaluates a candidate of a communication route from its node to the destination node on the basis of the index value relating to a relay node on the communication route, and selects the communication route. In addition, Japanese Unexamined Patent Publication No. 2008-131574 presents a method in which in the case where a multi-hop network is configured using wireless stations (nodes) having a cognitive communication function, when an end-to-end communication route is selected, an impact of frequency channel interference of a newly-switched node on peripheral nodes caused by switching the communication route is reduced.